PART II. CHAPTER XXII. 



Horizontal Silurian Strata. 



Fig. 282. 



A, Simmsii, portion of the shell at a, Fig. 281., natural size, 

 showing the tube and its radii within the siphuncle. 



vered at Castle Espie, in the county of Down, in Ireland. (See 

 Figs. 281, 282.) 



Silurian strata occasionally horizontal. The Silurian strata 

 throughout a large part of the province of Skaraborg, in the 

 south of Sweden, are perfectly horizontal ; the different subor- 

 dinate formations of sandstone, shale, and limestone, occurring 

 at corresponding heights in hills many leagues distant from each 

 other, with the same mineral characters and organic remains. 

 It is clear that they have never been disturbed since the time of 

 their deposition, except by such gradual movements as those by 

 which large areas in Sweden and Greenland are now slowly and 

 insensibly rising above or sinking below their former level. The 

 ancient limestone and shale; also of the Canadian lake district 

 before mentioned, are for the most part horizontal. 



These facts are very important, as the more ancient rocks are 

 usually much disturbed, and horizontality is a common charac- 

 ter of newer strata. Similar exceptions, however, occur in re- 

 gard to the more modern or tertiary formations which, in some 

 places, as in the Alps, are not only vertical, but in a reversed 

 position. These appearances accord best with the theory which 

 teaches that, at all periods, some parts of the earth's crust have 

 been convulsed by violent movements, which have been some- 

 times continued so long, or so often repeated, that the derange- 

 ment has become excessive, while other spaces have escaped 

 again and again, and have never once been visited by the same 

 kind of movement. Had paroxysmal convulsions ever agitated 

 simultaneously the entire crust of the earth, as some have ima- 

 gined, the primary fossiliferous strata would nowhere have re- 

 mained horizontal. 

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